A human version of the classic arcade game Pacman, superimposing the virtual 3D game world on to city streets and buildings, is being developed by researchers in Singapore.

Players equipped with a wearable computer, headset and goggles can physically enter a real world game space by choosing to play the role of Pacman or one of the Ghosts.

A central computer system keeps track of all their movements with the aid of GPS receivers and a wireless local area network.

The Human Pacman was developed by Adrian David Cheok and his team at the Mixed Reality Lab, National University of Singapore.

Merging different technologies such as GPS, Bluetooth, virtual reality, wi-fi, infrared and sensing mechanisms, the augmented reality game allows gamers to play in a digitally-enhanced maze-like version of the real world.

It has been selected as one of the world's top 100 high-impact and visionary technologies and will showcased at the Wired NextFest 2005 in Chicago, US, which runs from June 24 to 26.

Wireless updates

Combining both real and virtual elements, the game allows the human Pacman to 'see' virtual cookies with the aid of the special headset scattered on the street which the player can then 'eat' by walking through them.

The game as seen through the eyes of a player

Ghosts get to 'devour' the player by tapping them on the shoulder when they catch up to them within the game area.

In return, Pacman gets the ability to temporarily neutralise them and add to his virtual powers when he finds and picks up Bluetooth-embedded physical sugar jars scattered in the real world environment by a game coordinator.

The player's locations are also wirelessly updated to a virtual 3D Pac-world where online gamers can view their progress and participate by helping either Pacman or the Ghosts through text messaging.

Test runs were conducted on the university campus within a 70m by 70m game zone. With a four-player minimum, a typical game was played out in about 10 to 20 minutes.

Other institutions focused on creating similar games include the University of Southern Australia, which has developed an augmented reality (AR) version of the Quake game.

Alternate reality

Accuracy and positioning are some of the major challenges facing researchers creating deployable AR versions of complex games.

"Most attempts at AR games, like AR Pacman or AR Quake, rely on having very accurate models of the physical world such as the trees, cars, buildings, etc. which is practically impossible," said Blair MacIntyre, Director of the Augmented Environments Lab at Georgia Tech.

The main challenge of course lies in placing the models in the right place, so that, for example, we won't see a Pacman walking into the wall of a castle

Adrian David Cheok, Mixed Reality Lab

"First, the world is just too complicated, and second, it changes too much - cars and people move, trees grow, etc."

The research team at Singapore says though that a totally accurate real world model is not necessary.

"What we seek is to create an alternate version of representing the real-world by some fantasy landscape," says Mr Cheok.

"An office blocked could be replaced by a castle. We do not really need to have an accurate model of the environment, just a rough gauge will do.

"The main challenge of course lies in placing the models in the right place, so that, for example, we won't see a Pacman walking into the wall of a castle."

With current positioning technologies, this kind of accuracy is still a major issue. Typical GPS receivers have an accuracy of about 10 to 30 meters, but for a flawless gaming experience augmented reality games need the error margin to be within the millimetre range.

Tracking players also becomes impossible when they get too close to high-rise buildings that block GPS signals.

Commercial games

To combat these issues, the Singapore team selected a wide open space as the game area and with advanced Long Range Kinematic (LRK) GPS technology they say they are able to maintain a maximum error level of 30 cm.

The more conventional way to play Pacman

If a player's position is lost, the system tries to get the player's orientation through a digital compass, detect the number of steps taken, and predict their current position.

"This is by no means a foolproof method, as the errors do accumulate," says Mr Cheok. "However, it does serve as a feasible temporary solution in case of GPS-signal loss."

However the real drawbacks to creating commercial AR games are the costs involved.

An entire system costs anywhere from $10,000 to $20,000. It is expected to take a number of years before the technology can be truly affordable to the average gamer.

Some of the AR gaming technology developed at the University of South Australia is being modified for consumer use.

The researchers have created a start up company called A-Rage that plans to launch augmented reality game engines into market with a target price tag of AUD$500, by the end of 2006.

Experts believe AR technology will revolutionize the gaming experience creating an arena where people move about, socialising and interacting with each other instead of being glued to a computer screen.

"These games symbolize the dawn of an era where real and virtual interactive experience will form part of the routine of our daily lives, allowing users to indulge in the seamless links across different domains be it for entertainment or socialising," says Mr Cheok.